In conventional color film development, color film consists of multiple layers each sensitive to a different color of light. These layers contain grains of silver halide. Photons of colored light appropriate to each layer render the grains reducible to elemental silver upon the application of a developing agent. Contained within the primary developer for negative films and in the secondary color developer for reversal, or color positive, films are couplers that combine with the reaction products of the silver halide reduction and with other couplers contained in each layer to produce specific dyes within the film. These dyes form around the developing silver grains in the film and create dye clouds. Following color development, any remaining milky white unexposed silver halide is washed away in a "fix" solution and the reduced black grains of silver are washed away in a "bleach" bath. Usually the fix and bleach baths are combined into one. After all the silver is removed, a clear film remains with colored dye clouds articulating the colored image.
In a color negative film, the first and only developer contains couplers to form a negative dye image at the same time as the negative silver image develops. The bleach-fix bath then removes both the developed silver and the undeveloped silver halide leaving only the negative color dye image. In color positive film, sometimes called transparency or reversal film, the first developer does not contain couplers. This first developer uses up the exposed silver halide in areas of the film that were exposed leaving silver halide in areas of the film that were not exposed. This remaining silver halide is rendered developable either by exposing it to bright light or to a fogging chemical. A second developer that does contain couplers then reduces this remaining silver halide to silver producing at the same time a dye image. The silver halide remains, and the dyes form, in areas of the film that did not receive light while no silver halide remains, and therefore no dyes form, in areas of the film that had originally received light. Thus, a positive image is formed for direct viewing following the fix and bleach steps.
In electronic film development (a method of developing film without forming dyes), the developing film is scanned at a certain time interval using infrared light so as not to fog the developing film, and also to see through antihalation layers. During development, color is derived from a silver image by taking advantage of the milky opacity of unfixed silver halide to optically separate the three color layers sensitive to blue, green, and red. This application will follow a convention of referring to the top of the three layers of the film as the "front" and the bottom layer closest to the substrate as the "back" or "rear". Viewed from the front during development, the front layer is seen clearly, while the lower layers are substantially occluded by the milky opacity of the front layer. Viewed from the rear during development, the back layer is seen, while the other layers are mostly occluded. Finally, when viewed with transmitted light, the fraction of light that does penetrate all three layers is modulated by all, and so contains a view of all three layers. If the exposures of "front", "back", and "through" views were mapped directly to yellow, cyan and magenta dyes, a pastelized color image would result. However, in digital development these three scans, "front", "back" and "through", are processed digitally using color space conversion to recover full color.
One problem with prior methods of electronic film development is that the film is typically consumed in the process. Because the developer chemicals used during typical electronic film development do not contain couplers, color dye clouds are not formed in the film. The lack of dye clouds renders the film useless once the traditional electronic film development process is complete. The present invention addresses this problem by providing a conventional color negative as a byproduct of electronic film development.